A typical scroll compressor has a first scroll member which has a spiral wrap located on one face thereof, a second scroll member which has a spiral wrap located on one face thereof with the spiral wraps of the scroll members being intermeshed with one another, and means for causing the first scroll member to rotate on a separate axis with respect to the second scroll member whereby the spiral wraps will create pockets of progressively decreasing volume from a suction zone to a discharge zone.
The means for causing the first scroll member to rotate on a separate axis with respect to the second scroll member is in many cases an electric motor. These electrical motors can be equipped with thermal protection devices to stop the operation of the motor when an over temperature condition exists. These thermal protection devices are normally a temperature sensor or sensors which are located within the proximity of the windings of the motor. When the temperature sensor or sensors encounter an over temperature condition, a signal is sent to a control device to stop the operation of the motor. On larger compressors or the higher horsepower compressors, three phase electrical current is supplied to the electric motor. For these three phase electrical compressors, a separate temperature sensor can be imbedded within the windings for each phase of current. These three temperature sensors are then wired in series such that any one of the individual phase windings could signal the control device to stop the operation of the motor due to an over temperature condition.
When solid state motor protection controls are employed, thermistors can be used for the temperature sensors. A thermistor is a resistive circuit component having a high positive temperature coefficient of resistance (as temperature increases, resistance also increases). The resistance of the thermistor or the series of thermistors is monitored by the solid state motor protection controls and upon reaching a threshold value, the controls will trip a relay to shut down the electrical motor and thus the compressor.
A typical scroll compressor, when operating, can generate excessively high discharge gas pressures due to the compressor functioning at a pressure ratio much greater than that which is designed into the machine in terms of its predetermined fixed volume ratio. These excessive discharge pressures can be caused by many different field encountered problems including loss of working fluid charge, blocked condenser fan in a refrigeration condition, or for a variety of other reasons. The excessively high discharge gas pressures will in turn cause excessively high discharge gas temperatures. If the compressor is allowed to continue to operate in these conditions, damage to the compressor will result.
Various prior art methods have been developed to monitor the temperature of the discharge gas and to shut the compressor down when excessive temperatures are encountered. These prior art methods include creating a leak from the high side of the compressor to the low side of the compressor of the high temperature discharge gas. This high temperature gas raises the temperature of the motor components including the standard type of thermal motor protectors described above which will then signal a control device to shut the motor down. Variations of the above designs include the incorporation of funnels or tubes to direct the high temperature discharge gas to specific motor components to improve the performance of the safety system. The problem associated with these designs is that there is an inherent delay in responding to the increase in discharge gas temperatures as the various motor components heat up sufficiently to cause the thermal motor protectors to signal the control device.
Another prior art method of monitoring the temperature of the discharge gas is to position a temperature sensor within the discharge area of the scroll compressor. The lead wires from this sensor are directed through the hermetic shell of the compressor to an outside control unit which will shut down the compressor when a specified discharge gas temperature is experienced. While this prior art method eliminates the inherent delay in the reaction to the increased gas discharge temperature, the penetration through the hermetic shell to provide access to the temperature sensor is a costly and troublesome design. The penetration of the shell requires additional sealing in order to maintain the integrity of the hermetic shell and once the temperature sensor's lead wires are outside the shell, additional control connections are required by the user.
Another prior art method of monitoring the temperature of the discharge gas is to position a temperature sensor on the exterior of the shell as close as possible to the discharge area of the scroll compressor. In order to position the sensor as close as possible to the discharge area, prior art compressor assemblies are provided with a deep drawn cup on the upper portion of the shell which extends into the discharge area. The temperature sensor is then positioned at the bottom of the deep drawn cup on the exterior of the shell. While this prior art design eliminates the need for additional penetration of the shell and shortens the delay in responding to the increase in discharge gas temperatures, there still is a significant amount of delay in responding to the higher temperatures due to the shell acting as a heat sink.
Accordingly, what is needed is a system for monitoring and reacting to the temperature of the discharge gas of a scroll machine which has the improved ability to track actual compressor temperatures. The system should not require any type of additional shell penetration or additional control connections by the user and should be manufacturable at a relatively low cost.
The present invention provides the art with a thermal protection system for a scroll machine which overcomes the above mentioned disadvantages of the prior art systems. The present invention comprises a temperature sensor which is positioned directly within the discharge port of the scroll compressor. The lead wires from the temperature sensor are wired in series with the normal motor temperature sensor circuit to provide the scroll discharge temperature control function as an integral part of the motor temperature control system located within the hermetic shell of the compressor. An additional embodiment of the present invention not only detects discharge gas temperatures but it also has the ability to detect the actual temperature of a selected compressor component. The present invention thus provides the improved ability to track actual scroll compressor temperatures and react to these temperatures without having the requirement of additional shell penetration and without requiring additional control connections by the user. The entire system is incorporated within the interior of the hermetically sealed shell at a relatively low cost.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.